disable gravatar in test (#32529)

When running e2e tests on flaky networks, gravatar can cause a timeout
and test failures. Turn off, and populate avatars on e2e test suite run
to make them reliable.

services/repository/contributors_graph_test.go

@@ -18,6 +18,7 @@ import (
 
 func TestRepository_ContributorsGraph(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())
+
 	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 2})
 	assert.NoError(t, repo.LoadOwner(db.DefaultContext))
 	mockCache, err := cache.NewStringCache(setting.Cache{})
@@ -46,7 +47,7 @@ func TestRepository_ContributorsGraph(t *testing.T) {
 
 	assert.EqualValues(t, &ContributorData{
 		Name:         "Ethan Koenig",
-		AvatarLink:   "https://secure.gravatar.com/avatar/b42fb195faa8c61b8d88abfefe30e9e3?d=identicon",
+		AvatarLink:   "/assets/img/avatar_default.png",
 		TotalCommits: 1,
 		Weeks: map[int64]*WeekData{
 			1511654400000: {